Diversity receiving is well known in the field of communications. There are several types of switched diversity including temporal and spatial switched diversity. In temporal diversity, the same signal is transmitted at two different times. For example in a time division multiple access/time division multiplexed (TDMA/TDM) system, the same signal would be transmitted in time slot 0 and time slot 1. The expectation here is that the interference will vary with time and one of the signals will be received better than the other. The receiver determines which signal was the best and processes that signal.
In spatial diversity, the same transmission is received at two different locations. Again, the expectation here is that the received signals will have taken different paths to the two locations and will have different interference effects. The receiver will determine which signal is the best and process that signal.
A variation of spatial diversity is using two antenna to measure other transmissions on the frequency that carries the signal of interest to the receiver. These measurements are then used to select an antenna to be used for reception of the desired signal.
One drawback of measuring other transmissions in a switched diversity process is that power is consumed by the receiver in order to make these other measurements. Even though the receiver is only interested in one signal transmitted on one channel, two other signals on two other channels must be measured to make the diversity decision. Therefore, this type of selection requires the use of additional power when making the measurements. In portable RF equipment, power consumption is a key concern. Therefore, it would be desirable to provide a portable RF receiver which would minimize the power consumed in performing the diversity function.